Presbyopia is a visual condition in which the lens of the eye loses some elasticity. When this condition occurs it causes defective accommodation and inability of the eye to focus sharply for near vision such as is required for reading. This condition is more commonly known as farsightedness. Presbyopia typically manifests itself as a person enters middle age.
Thus, persons who suffer from presbyopia are accommodated by aids such as spectacles, which employ relative distance magnification which enable these people to view an object which is close to them. Such aids essentially operate by bringing the object to be viewed closer to their eyes to create an enlarged retinal image.
Spectacles which accomplish relative distance magnification are commonly referred to as bifocal spectacles. Such devices are very well known in the art and include a bifocal lens arrangement. As is well known in the art, a major portion of a bifocal lens includes the person's normal prescription which optimizes the person's far or distant visual acuity. In the lower portion of the bifocal lens is a "bifocal" segment which provides a positive magnification for enabling the person to maintain a clear focus at a near working or reading distance.
Many people who use bifocal spectacles are employed in occupations which involve precision work performed at an arms length distance. Examples of such occupations include surgeons, dentists, and machinists.
In the performance of such work it is often desirable to magnify the work area. The prior art has responded to this need by providing spectacles with a pair of telescopes. In the prior art arrangement shown in FIG. 1, each telescope 26 and 28 is attached directly to its respective carrier lens 14 and 16 of the spectacles 10. The arrangement shown in FIG. I is essentially of the type sold by Designs for Vision, Inc., the assignee herein, under the name BIOPTIC TELESCOPES.
In the prior art arrangement shown in FIG. 1, each bioptic telescope 26 and 28, also known as a Galilean telescope, is received by a hole drilled in its associated carrier lens. The telescopes are generally oriented in the carrier lens such that the optic center of the ocular lens of the telescope is Just below the top of the carrier lens. The holes drilled in the carrier lens are drilled at a slightly upward angle from the horizontal plane. Such an arrangement positions the telescopes out of the user's line of vision. Since the upper segments 18 and 20 and respective bifocal segments 22 and 24 of the lenses 14 and 16 are generally configured for the user's normal and reading prescriptions respectively, the user is capable of using the spectacles 10 conventionally for general work or reading. When the user needs magnification for distance spotting via the telescopes, the user must drop or tilt his head to bring the telescopes into alignment with his eyes and the work area or object to be viewed. When the user wants to view through either the upper or bifocal segments of the lens again, the user must then raise or tilt his head back to bring the lens into alignment with his eyes again for normal viewing. The degree of head tilting needed when switching between the telescopes and the bifocal segment of the lens is much more pronounced than is required to shift between the upper segment of the lens and the telescopes. Consequently, the user must make a very deliberate change in the position of his head in order to accomplish the switch.
This continuous dropping and raising of the user's head to view through either the telescopes or the carrier lens of prior art designs is physically tiring and cumbersome. This is especially true for example, during surgical procedures where the surgeon must look down at the work area at one moment and then look up at life support monitors and/or nurses at another moment.
Further, since the arms-length work area is typically located at waist level, the user must tilt his or her head downwardly at an angle in order to view the work area. When using the earlier described prior art telescopes, the upper location of the telescopes in the lens requires the user to tilt his or her head at an even greater angle which is unnatural and uncomfortable. This unnatural posture can eventually lead to the user acquiring neck and back problems.
The above-described arrangement further requires that the spectacles be dedicated exclusively for use with the telescopes, since the lenses are drilled to receive the telescopes. Thus, when the user wishes not to have the benefits or the cosmetic look of the telescope arrangement, the user must also have a second pair of conventional spectacles.
Other prior art arrangements are known to exist whereby the telescopes are not attached directly to the carrier lenses. An example of such an arrangement is disclosed in U.S. Pat. No. 296,337 issued to Caplan on Jun. 21, 1988. In the arrangement disclose therein, the telescopes are pivotally attached to the spectacle frame. When the user wishes to view an object through the telescopes, the user pivots the telescopes down in front of the lenses. When the user wishes to view conventionally through the spectacles, the telescopes are pivoted up and away from the lenses.
The inventors herein have studied the advantages and the disadvantages of the prior art designs and have determined that it would be desirable to have detachable telescopes which are not mounted directly to the lens. Such a configuration would allow the spectacles to be used without the telescopes if desired. The inventors have further determined that it would be desirable to orient the telescopes in front of the lower portion of the lenses or in front of the bifocal magnifying lenses. Orienting the telescopes in front of this area of the lenses eliminates the need for the user to tilt his head downward in order to view the waist level work area, thus providing a more natural head tilt angle. Moreover, the orientation of the telescopes in this position allows the user to view a monitor or talk with an assistant, by merely looking up from the work area without having to move or tilt his head.
Merely orienting the telescopes in front of the lower portion of the lenses, however, presents a particular problem when the spectacles are bifocal. The telescopes used in prior art arrangements are afocal in nature. A telescope which is afocal in nature is generally one that allows a person to view an object through the telescope without having to focus the telescope. When an afocal telescope is Viewed through the bifocal segment of a bifocal lens, the afocal nature of the telescope is cancelled via the bifocal segment.
Thus, it is a primary object of the present invention to provide a detachable afocal telescope arrangement for bifocal spectacles which can be viewed through the bifocal segment of the spectacles without losing the telescope arrangement's afocal characteristics.